1. Field of the Invention
The present invention relates to a rolling bearing device having a sensor for detecting vibration (acceleration), temperature, rotational speed, humidity (moisture) and the like, and a ring with the sensor for used with the rolling bearing device.
2. Description of the Related Art
The rolling bearings, which are used for reducing rotation resistance, have been used in various fields, such as industrial equipment, vehicles, airplanes, and power plants. The rolling bearing will be vibrated when the rotating shaft is eccentric and be heated through the rotation friction. The vibration and temperature will adversely affect the lifetime of the bearing. In some of industrial machines, a water-soluble cutting lubricant is frequently used in machining work. Accordingly, sometimes the bearing part receives a splash of it, which contains water. When the rolling bearing is mounted on a machine used outdoors, such an automobile, a railroad car, or a construction machine, the bearing is frequently splashed with water when it runs in the rain or on a road with puddles. A measurement which has been taken for preventing the rolling surfaces of the raceway and the rolling elements from rusting is to use water-proof shields made of rubber or the like, which is slidably fitted to the inner and outer rings. Even in the case of the bearing having the water-proof shield, when weather conditions change, in particular when temperature rapidly changes, water enters the inside of the water-proof shield in the form of vapor, so that dew condensation will form on the rolling surfaces of the raceway and the rolling elements, sometimes.
Particularly, in the case of the rolling bearing, which is mounted on a position where its inspection is difficult, e.g., a device interior position, the vibration, temperature, rotational speed or humidity sensors as general-purpose parts are separately provided. A sensor suitable for a rolling bearing to be used is selected from among those sensors, and attached to the outer peripheral surface of the bearing. A signal derived from the sensor thus attached is led out to a necessary part by way of a wire.
Specifically, a general-purpose vibration sensor including an acceleration meter, a general-purpose temperature sensor including a thermocouple, a rotational speed sensor including an encoder and the like are connected, by wires, to an instrument mounted on a housing which accommodates the rolling bearing device. In this case, vibration, temperature and rotational speed of the bearing are indirectly detected through the housing. There is a proposal in which those general-purpose sensors are mounted on the rolling bearing, and signals representative of vibration, temperature and rotational speed are directly detected. In this case, a space used for mounting the sensors is formed in advance in the housing or the shaft.
Threshold values are set for the vibration and temperature. When the measured vibration and temperature exceed the threshold values, signals representative of those measured ones are output to the instrument.
Those general-purpose sensors are large in size. Because of this, a rolling bearing to which the sensors are mounted has a large protruded part at which the sensors are mounted. The protruded part is likely to restrict a freedom in laying out parts. Allowing for this, it is necessary to determine a configuration of the bearing and the layout of the sensors. The wiring ranging from those sensors to the instrument is also required. To mount those bearings with sensor, the machining work of the housing and the shaft increases.
In a case where the existing equipment, e.g., industrial equipment, is automated, it is essential to grasp a running status of the automated equipment in a remote control manner. When changing the bearing in the existing equipment into a bearing with sensor, it is required to greatly alter the bearing and its vicinal structure since the conventional bearing with sensor is not interchangeable with another. Some types of shafts reject the mounting of the sensors thereon. A case where the sensor is not directly attached to the bearing but is located near the sensor, suffers from some problems as described below.
The vibration sensor is constructed mainly with an accelerometer, and its detection has a directivity. Accordingly, when it is located apart from an object to be detected, the detection is likely to contain noticeable noise. In the case of the temperature sensor, with increase of a distance of the sensor to a heat source, its thermal conduction time becomes longer, and the sensing operation is affected by another heat source or sources, resulting in producing an incorrect sensed value. Also for the humidity detecting, it is necessary to detect humidity within the bearing space located inside the bearing; otherwise, it is impossible to correctly evaluate a degree of water entrance.
In addition, to detect a rotational speed of the rotating shaft used in industrial equipment, machine tool, vehicle and the like, an encoder is frequently attached to the shaft. In this case, the encoder is used for a sensor for detecting a rotational speed for the purpose of controlling the rotational speed of the shaft. Further, a sensor for detecting vibration or temperature is provided for monitoring an operating condition of the bearing and the device including the bearing.
The encoder for detecting a rotational speed of the shaft and the sensor for detecting vibration or temperature receive electric power from a power source, which is separately provided. Further, the detected signals of the rotational speed, vibration, temperature and the like are outputted by wires.
In this case, wires must be used for supplying electric power from the separately provided power source to the encoder for detecting a rotational speed of the shaft and the sensor for detecting vibration or temperature. Those wires must be taken out every time the maintenance or replacement of the bearing and its vicinal portion is carried out. A complicated mechanism is required for supplying electric power to the sensor provided on the rotating part.
To avoid this, the power source is preferably incorporated into the bearing. An example of the bearing containing an electric generator therein is disclosed in JP-A-6-200929. The electric generator includes a comb-shaped iron core having a plurality of threads radially arranged from the inner part of the bearing toward the outer part, a coil wound around the bottoms each between the adjacent threads, a plurality of magnets located while being confronted with the bottoms of the iron core, and a ring which has cuts arranged at intervals equal to the threads of the iron core and rotates at a speed equal to that of the bearing between the iron core and the magnets. When the ring rotates between the iron core and the magnets, magnetic lines developed from the magnets are induced into the ring to excite the threads of the iron core, whereby the rotating speed is detected and electric power is generated.
In the electric generator disclosed in JP-A-6-200929, since the iron core extends over a part of the circumference, the electromotive force generated by it is small. Further, the electric power generated by the electromagnetic induction is caused by the magnetic flux. Accordingly, an accuracy of the rotational speed detection will be degraded by ring cutting accuracy, magnet layout accuracy, non-uniformity of magnetic forces of the magnet, dispersion of the gap between the iron core and the ring and dispersion between the ring and the magnet, which is caused by an eccentricity of the ring, and the like. Further, the electric power generated is instable.